In general, a power supply includes a power factor correction (PFC) unit and a pulse wave control unit, or further includes a stationary power control unit, and all of the units are integrated into several different integrated circuits (ICs) or into a single integrated circuit in order to save space and power loss. Further, a detection input voltage and a self-start function can be added to the integrated circuit, so that the integrated circuit can control a bias voltage power (Vcc) by detecting and determining whether or not the inputted alternating current of the integrated circuit has reached the operating voltage, and then the integrated circuit decides whether or not to start a circuit unit in the integrated circuit. If the inputted alternating current has not reached a normal operating voltage, the integrated circuit will shut automatically and repeat detecting whether or not the alternating current falls within the range of the normal operating voltage. The aforementioned prior art has been disclosed in R.O.C. Patent Publication No. 501830 entitled “Improved switching power supply”. Referring to FIGS. 2 and 3, a waveform 3 shown in FIG. 3 is the waveform of the voltage at node X as shown in FIG. 2. The traditional procedure of detecting an alternating current and starting up the integrated circuit includes the following steps:
The bias voltage power Vcc charges a capacitor C1, so that the voltage at node X rises to a start-up voltage for starting each unit of the integrated circuit. If the alternating current has not reached the normal operating voltage, then the load effect of starting the integrated circuit drops the voltage at the node X to a cut-off voltage value for shutting each unit of the integrated circuit, and then charges the capacitor C1 to the start-up voltage value again, and repeats the foregoing procedure until the alternating current reaches the normal operating voltage. Although the aforementioned operating mode of detecting the cycle of the alternating current can be predicted, yet the time for the alternating current to reach the normal operating voltage cannot be predicted, and thus the cycle for starting the integrated circuit differs from the cycle of normally inputting the alternating current normal, and the difference of cycles may cause a too-short buffer time for a system boot, and the surge may damage components. On the other hand, the voltage at node X will drop to the cut-off voltage value and then will shut the integrated circuit if an overload occurs suddenly in a normal operation. As a result, the load effect of the integrated circuit is eliminated, and the alternating current remains at the normal operating voltage, and the voltage at node X rises to the start-up voltage value again. The voltage drops again due to the overload, and the integrated circuit repeats the starting and shutting processes quickly during the period of detecting alternating current and overload. As a result, a large power loss and an overheat occur, which will directly affect the life expectancy of the integrated circuit. Obviously, the conventional control method and circuit require improvements.